The present invention relates to a method of producing a liner made of a low-carbon iron material to cover an explosive charge and allow carbon iron material formed by the method for such purpose.
Liners to cover explosive charges are generally composed of iron or copper. Copper is customarily employed for the liners of pointed cone shaped charges. The liner material should have high ductility and a high degree of purity to avoid the possible work hardening.
Many different materials have already been employed to produce liners to cover explosive charges.
Federal Republic of Germany published patent application DE-A 2,913,103, for example, discloses a liner for a flat cone shaped charge. This liner is made of an alloy which has a sufficiently high tantalum content to attain a density which is greater than that of copper. The alloy may contain further metals, such as tungsten, molybdenum or niobium. But then the required high ductility is no longer ensured.
Federal Republic of Germany published patent application DE-A 2,901,500 further discloses a liner material made of a superplastic alloy which is able to withstand great elongation without constriction until it breaks. The alloy is to be composed of lead and tin or zinc and aluminum.
Although these alloys have high ductility, they produce only an unsatisfactory power conversion in the target and a poor penetration depth in, for example, armor plates.
For liners made of iron materials, a technically pure low-carbon soft iron is generally employed which is available under the trade name Armco iron (American Rolling and Mining Company). The typical analysis of Armco iron reveals the following values, in percent by weight: 0.015% C, 0.02% Si, 0.002% Mn, 0.05% P; 0.022% S, 0.01% N; total impurities about 0.1%, and remainder Fe.
When refining raw iron, pure oxygen is added to the melt to convert the accompanying elements into slag. Oxygen then also goes in solution in the melt in the form of FeO. In this connection, an important dependency ratio applies, i.e., C.times.O=constant. A steel having a low carbon (C) content therefore contains a relatively large amount of oxygen after refining so that, due to its hot shortness sensitivity, it must be deoxidized by the addition of ferromanganese. Since this is not possible with Armco iron, the melt is subjected to vacuum degasification which is intended to reduce the oxygen content and improve structural homogeneity.
Nevertheless, Armco iron does not satisfactorily meet the requirements placed on a liner material to cover explosive charges. In particular, it is not possible to produce liners with reproducibly uniform behavior from different charges of Armco iron melted at different times since various anisotropies, coarse grains and rolling textures occur occasionally due to the cold work. These anisotropies are evident already, for example, in that if a flat disc is the final shape for a flat cone liner or a spherical cap-shaped liner shell, uneven surface structures (orange skin and pull grooves) develop. If such liners are explosively reshaped into elongate projectiles, the shaping velocity is extremely high so that even the smallest inclusions have a significantly greater influence than in customary test shaping, and projectiles made of Armco iron often have an irregular, asymmetric appearance and form crooked projectiles which tend to tear off during projectile formation, thus resulting in unsatisfactory performance in the target.